Image orthicon pickup tube using metal evaporator filament to deflect return beam



Jam 3,1M1967 K. FRANK 3,296,485

IMAGE ORTHICON PICKUP TUBE USING METAL EVAPORATOR A FILAMENT TO DEFLECT RETURN BEAM Filed Dec. 10, 1963 2 Sheets-Sheet 1 Fig.7 PRIOR ART Inventor: Kurt Frank Attorney u Jan: 3, 1967 K. FRANK 3,295,485

IMAGE ORTHICON PICKUP TUBE USING METAL EVAPOHATOR FILAMENT TO DEFLECT RETURN BEAM Filed Dec. 10, 19631 2 Sheets-Sheet 2 Fig. 3

Jn van/or: Kurt Frank IMAGE ORTHICON United States Patent PItJKUP TUBE USING METAL EVAPORATOR FILAMENT. T0 DEFLECT RE- TURN BEAM" 1* Kurt Frank, Darmstatlt, Germany, assignor to Robert Bosch G.m.b.H;, Stuttgart, Germany Filed Dec. 10, 1963, Ser. No. 329,520 1 Claims priority, application figrmany, Dec. 20, 1962,

33, 2 Claims. ((1315-11) The main object of the present invention is to improve thei resolution of image orthicon pickup tubes including.

field} mesh electrodes.

One object of the invention is to provide a method of improving the resolution of an image orthicon tube by introducing a determined auxiliary deflection field.

Further objects of the invention concern construci tions of image orthicon tubes with improved resolution comprising determined deflection means.

In theoperation of image-orthicon pickup tubes a defectin thederived picture results from the fact that owing to thescanning movement on the first dynode to which the deflection fields give rise, the electron beam returning from the. target impinges from time to time on the aperture through which the scanning beam emerges. When thlSOCCUX'S, no secondary electrons are released and a bright spot therefore appears in the picture. This phenomenonyknown by the name of .spotlight effect, has

been observed even in the earlier image orthicon tubes Withoutyfield mesh electrodes.

In earlier types of tubes without field mesh the pattern traced upon the gun anodewhich acts simultaneously as first dynode of the multiplier systemhas a considerableextent, so that the relative width of the spot was small} and therefore the spotlight effect itself not very disturbing. The position of the. spot was found to be accidentally. dependent on non-controllable tolerances of the tube elements.

For avoiding the spotlight effect it has been proposed in :image orthicon pickup tubes to produce by means of two plates held at constant potentials an electrostatic field through which the pattern scanned on the first dynode by the returning electron beam is shifted sufficiently to ensure thatHthe aperture in the diaphragm lies outside the area covered by the pattern. In. this case, no disturbing white spotis to be observed. In fact, the use of these deflector plates has been abandoned in the course of the further improvement of the image orthicon, since their presence gave rise to other constructional difficulties. Instead, one ofsthe electrodes of the electron-optical imaging system was slanted on itselectron-optically effective edges so thataa deflection of the raster sufiicient to abolish the undesired effect was produced.

An electrode of this form was introduced into fieldmesh tubes, where it served at the same time as deceleration electrode (suppressor) for suppressing secondary electrons released at the field mesh by the impact of electrons inthe scanning beam.

As a result of the increasing demands upon the image orthicon pickup tube, however, it is sought to effect an increase in the resolution such that the picture quality maybe matched to the full capacity of the television transmission channels. It has been found that the existin gresolution of the pickup tube, that is, some 55 to 60 percent of the peak white amplitude measured at a black toi-whitei transition is available at 5 mc./s. no longer meetsthese demands.

In an examination of the electron-optical imaging con ditionsof image-orthicon tubes with field mesh, which was based upon the observation of a scanning pattern burnt on to the first dynode when the tube was overloaded, it

3,296,485 Patented Jan. 3, 1967 was found that the shift of the scanning pattern resulting from the slanting of the lens electrode mentioned above, which in the field-mesh tubes served also as the suppres' sor for suppressing the secondary electrons, is much greater than would be necessary for the abolition of the spotlight elfect, while without a shifting field the center of the scanned pattern coincides approximately with the aperture of the gun anode. Although such field mesh tubes are already commercially available, these facts have obviously been overlooked. In point of fact the existing tubes of this kind are equipped with a suppressor electrode of which the electron-optically effective edge is made to slant at an angle of 13 degrees.

In carrying out the invention it had to be taken into account that the construction of the image orthicon pickup tube is already practically standardized, so that neither could additional conductors be led into the tube, nor could substantial alterations be made to the lens electrodes of the electron-optical imaging system. It was there fore not possible to consider adopting the course of producing the necessary deflection field, not by the device described above but by an additional electrode which would be connected by way of an individual lead-in con nection with an adjustable potential. An alteration of the tube base by the inclusion of an additional connecting pin would make the tube unsuitable for use in existing cameras and would therefore entail a re-development of the cameras also.

According to the present invention there is provided an image orthicon television pickup tube including a field mesh electrode and an apertured gun anode, which acts also as collector electrode for the return beam and as first dynode, in which there is superimposed upon the field of at least one electrode of the electron-optical imaging system an electrostatic field effective in the direction perpendicular to the axis of the electrode system and perpendicular also to the direction of line scanning, the intensity of said electrostatic field being such that the aperture in said gun anode lies outside the scanning pattern traced on said anode by said return beam and at a distance from the edge of said pattern which does not exceed 0.5 millimeter. Preferably the distance of the aperture from the edge of the scanning pattern does not exceed 0.2 millimeter.

In image orthicon pickup tubes constructed in accordance with the invention the resolution at 5 mc./s. may be improved from 50-60 percent of the black-to-white transition to -90 percent, without the bright spot becoming apparent. This improvement is effected, it appears, because the transverse component of the electric field which is employed for shifting the raster is only just as large as is necessary to avoid the bright spot, and the symmetry of the electron-optical imaging system is thus distorted only so little that practically no astigmatism is produced in the lens fields. In addition, in pickup tubes according to the invention the deflection of the scanning pattern is effected in the direction of vertical deflection. In general, the pattern scanned on the first dynode does not in fact have the same aspect ratio as that scanned on the target, but is compressed in the direction of vertical deflection. If, therefore, the shift of the scanned pattern on the first dynode were to be effected in the direction of line deflection, then a considerably greater asymmetry of the lens field would be necessary to produce the required shift and this would yield a greater loss of resolution in the picture.

In order that the invention may be readily carried into effect, it will now be described with reference to the accompanying drawings, given by way of example, in which:

FIG. 1 is a schematic illustration of the more impor- 3 tant electrodes of the electron gun portion of known image orthicon pickup tubes;

FIG. 2 shows the form of an improved lens electrode which may be used in an image orthicon pickup tube according to the present invention;

FIG. 3 shows in partly sectional side elevation the constructional arrangements of the electron gun portion of one embodiment of image orthicon pickup tube according to the present invention, including an auxiliary electrode for producing the desired shift;

FIG.4 shows an end view of the electrode system shown in FIG. 3.

In FIG. 1, 1 is the envelope of an image orthicon pickup tube, to the foot 2 of which the electrodes of the gun are connected, and 3 is an electron source of which the details are not shown as it may be of the construction conventional in this art. It contains in known manner a thermionic cathode and a modulator electrode and in addition carries the first dynode 4 of an electron multiplier 5. The dynode 4 is pierced at its centre by a very fine aperture through which the electron emerges from the gun to pass towards the field mesh 29 and the target 30. In the direction of the emergent beam there are then found a persuader electrode 6, a screen electrode 7 and a suppressor electrode 8. The electrode 6 serves to guide the secondary electrons released by the first dynode 4 into the electron multiplier 5. The electrode 7 is connected to a wall coating 9. The electrode 8 is of particular significance. Its known purpose is to prevent secondary electrons released from the field mesh in front of the target (not shown) from entering into the gun system of the pickup tube and it is therefore held at the potential of the gun cathode. The wall electrode, which forms a space substantially free from electrostatic fields within which the electron beam is subjected to magnetic deflection fields, terminates at the suppressor electrode.

As already discussed, in known tubes the suppressor electrode is provided with edges sloping at 13 degrees in order to ensure that the beam returning from the target is separated from the incident beam sufficiently to ensure that the scanning pattern traced on the first dynode by the returning beam does not fall upon the anode aperture. A suppressor electrode of this form is also used in which rejection of the secondary electrons initiating at the field mesh is effected by suitable potential conditions in the neighborhood of the field mesh.

It has been found that the resolution of this known tube is inadequate, so that an increase of resolution is desired. It was found that a lack of sharp focus of the scanning beam is responsible for the inadequate resolution and that this lack of focus is connected with astigmatism of the electron lens formed by the suppressor electrode. It has been found empirically that astigmatism due to this cause can be reduced to an amount which is no longer significant if, in accordance with the invention, the suppressor electrode is made with a slant substantially less than 13 degrees, namely some 4-8 degrees. In this case the disturbance of the symmetry of the electron lens is so small that no appreciable reduction of picture quality results. With this amount of slant it is found that the shift of the scanning pattern traced on the first dynode by the return beam is sufiicient to avoid the appearance of the beam aperture in the picture, so that by this new construction of the suppressor electrode there is provided an image orthicon pickup tube having a resolution which lies near the theoretically possible limit. This theoretical limit is determined by the inhomogeneity which is always present in the velocities of the electrons compn'sing the scanning beam.

In FIG. 2 is illustrated a suppressor electrode such as may be used in an image orthicon pickup tube in accordance with the present invention. It will be seen that this electrode has its edge turned towards the target slanted to the general plane of the electrode at an angle of only degrees.

FIG. 3 shows a partly sectional side view of the electron gun assembly of one embodiment of image orthicon pickup tube according to the present invention. The electrodes 11 to 17 are the annular mesh electrodes of the electron multiplier. The electrode 18 is the so-called persuader electrode, held at a potential of some 300 v., which guides the secondary electrons released from the first dynode by the return beam into the electron multiplier. The suppressor electrode, designated by 19, is held approximately at cathode potential and serves to prevent secondary electrons released from the field mesh from intruding into the electron gun system. In contrast to the form used in known image orthicon pickup tubes, this suppressor electrode is formed so as to be rotationally symmetrical and is not slanted, so that it effects practically no disturbance to the symmetry of the electron-optical imaging field. At the upper margin of the suppressor 19 is disposed an evaporator device 10 in the form of a wire lying in a plane perpendicular to the axis of the tube and encompassing some 60 to degrees of the circumference of the suppressor. The wire carries a silver bead. During the manufacture of the pickup tube the wire carrying the silver bead is heated so that a small quantity of silver is evaporated on to the target in order to lower its 00- eflicient of secondary electron emission.

In FIG. 3 the suppressor electrode 19 and the evaporator device are shown partly in section, so that a part of the lead 20 to the heater Wire 10 is not visible. This lead 20 is taken to the persuader electrode 18, so that during normal operation the evaporator device lies at this potential. By making use of the protruding evaporator device in the manner described above there may be produced an electrostatic field which to a certain extent intrudes past the margin of the suppressor electrode into the imaging space and there effects a very small deflection of the scanning and return beams. The advancing scanning beam is deflected by a small amount in a given direction and the returning beam is deflected by a similar amount and in the same direction, so that the desired shift of the pattern scanned on the first dynode may thus be produced.

The invention may also be carried out in other embodiments without departing in any way from the spirit of the present invention. For example, in cases where a suppressor electrode is unnecessary, the shift field may be produced in the neighborhood of another electrode, for example the screen electrode 24. Another component which encompasses the outer circumference of the suppressor electrode may also be disposed on the persuader electrode 19.

What is claimed and desired to be secured by Letters Patent is:

1. Image orthicon tube containing a gun system for generating a scanning beam of slow electrons with an apertured gun anode acting also as collector electrode for the return beam and as first dynode of a multiplier system, a field mesh on the side of the target facing the gun anode, a cylindrical electrode between field mesh and gun anode serving as suppressor to inhibit the secondary electrons released on the field mesh from reaching the gun anode, said cylindrical electrode being connected to an electrode of the tube of substantially negative potential relative to the field mesh, a metal evaporator encompassing a part of the circumference of the suppressor electrode and connected to an electrode of the tube having a potential different from that of said suppressor electrode, so that an auxiliary field in a direction perpendicular to the axis of the tube is superimposed upon the symmetrical field of the suppressor electrode, said metal evaporator being arranged in a spacing from said suppressor electrode, said spacing being chosen so that, due to the deflection effect of said metal evaporator on the electron beam, the minimum distance between the pattern traced upon the gun anode by the return beam and the aperture of the gun anode amounts to more than 0.2 millimeter and less than 0.5 millimeter.

2.1} Imageyorthicon tubecontaining a gun system for generating a scanning beam of slow electrons with an apertured gun anode acting also as collector electrode for the return beam and asfirst dynode of a multiplier system, a field mesh lion the side of the target facing the gun anode, a cylindrical electrode between field mesh and gun anode serving as, suppressor to inhibit the secondary electrons released on the field mesh from reaching the gun anode,

, said cylindrical electrode being connected to the potential of the gun cathode, a silver evaporator comprising a heater wire with a silver head on said Wire and two supporting conductors, one of; which being connected to an electrode ofthe tube of morepositive potential than the gun anode, said heater wire being arranged in the plane going through the electron-optically effective edge of the cylindrical suppressorelectrode; on theside facing the target andencompassing, a part of its circumference, said heater wire being arranged in a spacing of said suppressor electrode, this spacing being chosen so that, due to the deflection effect of said silver evaporator on the electron beam, the minimum distance between the pattern traced upon the gun anode by the return beam and the aperture of the gun anode amounts to more than 02 millimeter and less than 0.5 millimeter.

References Cited by the Examiner UNITED STATES PATENTS 5/1956 Weimer 3l5-1l 5/1959 Rotow 315--11X 

1. IMAGE ORTHICON TUBE CONTAINING A GUN SYSTEM FOR GENERATING A SCANNING BEAM OF SLOW ELECTRONS WITH AN APERTURED GUN ANODE ACTING ALSO AS COLLECTOR ELECTRODE FOR THE RETURN BEAM AND AS FIRST DYNODE OF A MULTIPLIER SYSTEM, A FIELD MESH ON THE SIDE OF THE TARGET FACING THE GUN ANODE, A CYLINDRICAL ELECTRODE BETWEEN FIELD MESH AND GUN ANODE SERVING AS SUPPRESSOR TO INHIBIT THE SECONDARY ELECTRONS RELEASED ON THE FIELD MESH FROM REACHING THE GUN ANODE, SAID CYLINDRICAL ELECTRODE BEING CONNECTED TO AN ELECTRODE OF THE TUBE OF SUBSTANTIALLY NEGATIVE POTENTIAL RELATIVE TO THE FIELD MESH, A METAL EVAPORATOR ENCOMPASSING A PART OF THE CIRCUMFERENCE OF THE SUPPRESSOR ELECTRODE AND CONNECTED TO AN ELECTRODE OF THE TUBE HAVING A POTENTIAL DIFFERENT FROM THAT OF SAID SUPPRESSOR ELECTRODE, SO THAT AN AUXILIARY FIELD IN A DIRECTION PERPENDICULAR TO THE AXIS OF THE TUBE IS SUPERIMPOSED UPON THE SYMMETRICAL FIELD OF THE SUPPRESSOR ELECTRODE, SAID METAL EVAPORATOR BEING ARRANGED IN A SPACING FROM SAID SUPPRESSOR ELECTRODE, SAID SPACING BEING CHOSEN SO THAT, DUE TO THE DEFLECTION EFFECT OF SAID METAL EVAPORATOR ON THE ELECTRON BEAM, THE MINIMUM DISTANCE BETWEEN THE PATTERN TRACED UPON THE GUN ANODE BY THE RETURN BEAM AND THE APERTURE OF THE GUN ANODE AMOUNTS TO MORE THAN 0.2 MILLIMETER AND LESS THAN 0.5 MILLIMETER. 